The invention relates generally to a gear transmission for lifting machines and, more particularly, to a gear transmission comprising at least a one step cylindrical gear transmission rotatably carried at least partly inside a rope drum and a planetary gear transmission coupled to the cylindrical gear transmission.
The term "cylindrical gear transmission" as used herein refers to a gear transmission consisting of gear wheels that are cylindrical and each of which has only one contact line or point with a following or preceding gear wheel. Cylindrical gear transmissions are therefore distinguished herein from "planetary gear transmissions", which consist of planet wheels, a sun shaft and a gear rim having an internal toothing. In such planetary gear transmissions all the planet wheels are simultaneously in contact with the sun shaft and also simultaneously in contact with the gear rim. Similarly, herein "cylindrical gear" refers to a cylindrical gear wheel.
A drawback of this type of cylindrical gear transmissions, which are known from the prior art, is that they are bulky, particularly, in the case of high torque transmissions. Another disadvantage of known cylindrical gear transmissions is that they are heavy when designed for high torque.
The prior art also has used planetary gear transmissions, but these are expensive in the case of low torques because of the large number of components required. At high running speeds, vibration problems and high dynamic forces occur in planetary gear transmissions. Uniform distribution of forces in the planetary gear is another difficult problem, which is accentuated especially at high speeds of rotation. A particular difficulty in planetary gear transmissions is the non-uniform load distribution resulting from the shape, centering and pitch deviation of the teeth rims.